1. Field of the Invention
The present invention relates to a vertical MOSFET device having a protector for preventing its breakdown due to heat increase or the like.
2. Description of the Prior Art
In FIG. 1, there is shown a conventional vertical MOSFET device, as disclosed in Japanese Patent Laid-Open Specification No. 60-258967. In this case, an n-type high resistance epitaxial layer 12 is grown on an n.sup.+ -type low resistance substrate 11, and p-type base region 13 having a conductivity type different from that of the epitaxial layer 12 is formed in an upper surface area thereof. An n.sup.+ -type source region 14 having the same conductivity type as that of the epitaxial layer 12 is formed in a central upper surface area of the p-type base region 13, and a p.sup.+ -type base contact region 15 is formed in the left side surface area of the p-type base region 13. An insulating gate film 16 is formed on the surfaces of the right side of the epitaxial layer 12, the p-type base region 13 and the overlapping part of the source region 14. A gate electrode 17 is then formed over the entire surface of the insulating gate film 16. A source electrode 18 is formed extending over the partial surfaces of the n.sup.+ -type source region 14 and the p.sup.+ -type base contact region 15. The gate electrode 17, the source electrode 18 and the semiconductor substrate 11 are connected to a gate terminal G, a source terminal S and a drain terminal D, respectively.
There is shown in FIG. 2 an area of safety operation (ASO) of the conventional vertical MOSFET device shown in FIG. 1. The ASO is defined by three characteristic lines 21, 22 and 23 which represent the limitations by the maximum current, the maximum consumption power and the maximum voltage, respectively.
In this embodiment, when an overload such a short circuit or the like is applied to the MOSFET device, an overcurrent flows in the MOSFET device beyond its safety operation rating to bring about a breakdown or destruction of the MOSFET device due to its temperature rise.
In order to prevent such a breakdown of an element or device due to the overload, a particular external protecting circuit is additionally required, which brings about cost increase and inconvenience for handling the element or device.